Changes of PM2.5 and O3 and their impact on human health in the Guangdong-Hong Kong-Macao Greater Bay Area

In recent years, the combined pollution of PM2.5 and O3 in China, particularly in economically developed regions such as the Guangdong-Hong Kong-Macao Greater Bay Area (GBA), has garnered significant attention due to its potential implications. This study systematically investigated the changes of PM2.5 and O3 and their associated human health effects in the GBA, utilizing observational data spanning from 2015 to 2019. The findings revealed a spatial trend indicating a gradual decrease in PM2.5 levels from the northwest to the southeast, while the spatial distribution of MDA8 O3 demonstrated an opposing pattern to that of PM2.5. The monthly fluctuations of PM2.5 and MDA8 O3 exhibited V-shaped and M-shaped patterns, respectively. Higher MDA8 O3 concentrations were observed in autumn, followed by summer and spring. Over the five-year period, PM2.5 concentrations exhibited a general decline, with an annual reduction rate of 1.7 μg m−3/year, while MDA8 O3 concentrations displayed an annual increase of 3.2 μg m−3. Among the GBA regions, Macao, Foshan, Guangzhou, and Jiangmen demonstrated notable decreases in PM2.5, whereas Jiangmen, Zhongshan, and Guangzhou experienced substantial increases in MDA8 O3 levels. Long-term exposure to PM2.5 in 2019 was associated with 21,113 (95% CI 4968–31,048) all-cause deaths (AD), 1333 (95% CI 762–1714) cardiovascular deaths (CD), and 1424 (95% CI 0–2848) respiratory deaths (RD), respectively, reflecting declines of 27.6%, 28.0%, and 28.4%, respectively, compared to 2015. Conversely, in 2019, estimated AD, CD, and RD attributable to O3 were 16,286 (95% CI 8143–32,572), 7321 (95% CI 2440–14,155), and 6314 (95% CI 0–13,576), respectively, representing increases of 45.9%, 46.2%, and 44.2% over 2015, respectively. Taken together, these findings underscored a shifting focus in air pollution control in the GBA, emphasizing the imperative for coordinated control strategies targeting both PM2.5 and O3.

recorded at 38.4 μg m −3 and 95.8 μg m −3 respectively 9 .Against the background of global climate change, atmospheric pollution attributed to PM 2. 5 and O 3 have emerged as a significant environmental and public health concern, given its profound impact on air quality, human health, and the global environment [10][11][12] .PM 2.5 and O 3 pose significant risks to human health, as they can irritate the respiratory tract, leading to symptoms such as coughing, wheezing, and shortness of breath 13 .These pollutants also have the potential to exacerbate preexisting respiratory conditions such as asthma and chronic obstructive pulmonary disease 13 .Moreover, they can penetrate deep into the lungs, causing inflammation and resulting in lung damage.Prolonged exposure to PM 2.5 and O 3 can lead to decreased lung function over time.Furthermore, epidemiological studies have highlighted the association between PM 2.5 and O 3 exposure and cardiovascular issues.These pollutants can enter the bloodstream, contributing to the development of heart diseases, including heart attacks, strokes, and hypertension 14 .Utilizing observed PM 2.5 data, Maji et al. 15 reported that in China, PM 2.5 -related hospital admissions due to respiratory and cardiovascular diseases in 2016 were 610,000 (95% CI 370,000-860,000) and 360,000 (95% CI 200,000-520,000), respectively.Additionally, the total morbidity estimates for asthma attack, chronic bronchitis, and emergency hospital admissions were 1,000,000 (95% CI 700,000-1,280,000), 990,000 (95% CI 500,000-1,440,000), and 120,000 (95% CI 60,000-180,000), respectively 15 .In a separate study, Zhao et al 16 employed meta-analysis method techniques to estimate O 3 -related health effects across China in 2018.Their findings revealed that the total number of all-cause, cardiovascular, and respiratory deaths attributable to O 3 were 178,529 (95% CI 90,584-346,912), 118,842 (95% CI 40,787-192,507), and 38,178 (95% CI 0-80,159), respectively.
In recent decades, the Chinese government has demonstrated a steadfast commitment to monitoring and mitigating air pollution, instituting a series of policies and measures aimed at enhancing air quality.Previous studies have indicated that the successful implementation of the "Air Pollution Prevention and Control Action Plan" since 2013 has resulted in a decline in PM 2.5 levels across China, with a reduction rate of 3.4 μg m −3 per year, particularly notable in regions such as BTH, central China, and northeast China had larger declines 17 .However, there has been a notable upward trend in the national average O 3 concentration, showing an annual increase of 3.4 μg m −3 per year, with more pronounced increases observed certain regions, including PRD 17.It is noteworthy that while PM 2.5 levels have decreased nationally, no significant change has been observed in the PRD, suggesting that PM 2.5 pollution in this area may still be at high levels 9,17 .The Guangdong-Hong Kong-Macao Greater Bay Area (GBA), encompassing nine cities in the PRD, Hong Kong, and Macao, stands as one of China's most economically robust regions.Despite its economic strength, the GBA lags behind other global Greater Bay Areas in terms of air quality 18 .Moreover, there has been increasing attention on atmospheric compound pollution characterized by PM 2.5 and O 3 in this region.To date, no comprehensive studies have been conducted to assess their impact on human health 19 .
Given the above concerns, the aim of this study is to examine the spatial distribution and temporal trends of PM 2.5 and O 3 in the GBA from 2015 to 2019, and to quantify their impact on human health.

Data source
This study utilized monthly PM 2.5 and MDA8 O 3 data from nine cities in the PRD, Hong Kong, and Macao spanning from 2015 to 2019.These data were obtained from two sources: https:// quots oft.net/ air/ and the monitoring results reports of the Guangdong-Hong Kong-Macao Pearl River Delta Regional Air Quality Monitoring Network (http:// gdee.gd.gov.cn/ kqjc/ index.html).The combined network comprises 61 air quality automatic monitoring stations, distributed throughout the GBA, including 11 in Guangzhou, 11 in Shenzhen, 8 in Foshan, 4 in Zhuhai and 4 in Jiangmen 4 in Zhaoqing, 5 in Huizhou, 4 in Zhongshan, 5 in Dongguan, 4 in Hong Kong, and 1 in Macao, as illustrated in Fig. 1.The annual mean concentrations of PM 2.5 and MDA8 O 3 per station were calculated by averaging the monthly mean values for all months of the year.Subsequently, the annual averaged concentrations for each city were determined based on all stations in this city.
Moreover, population data for the nine cities in the PRD, Hong Kong, and Macao for each year were obtained from the statistical yearbooks of the Guangdong Provincial Bureau of Statistics (http:// stats.gd.gov.cn/ gdtjnj/), the Hong Kong Census and Statistics Department (https:// www.censt atd.gov.hk/ sc/), and the Macao Census and Statistics Department (https:// www.dsec.gov.mo/ zh-MO/).

Health impact assessment
Many epidemiological studies on air pollution rely on Health Impact Assessment (HIA), a widely employed method for quantify the potential effects of various air pollutants, including PM 2.5 , PM 10 , SO 2 , NO 2 , CO, and O 3 , on human health 13.HIA involves determining the health risk for an individual when the concentration of a particular air pollutant exceeds a certain threshold, typically calculated based on the exposure-response coefficient (β).It's worth noting that the β value in assessing the health risks associated with long-term exposure to air pollution is typically calculated through epidemiological studies.These studies often analyze extensive population data, including individuals exposed to varying levels of air pollutants and their health outcomes, such as the number of people with cardiovascular or respiratory diseases.By statistically analyzing these data, the association between air pollution exposure and health issues can be determined.The β value is a crucial parameter derived from this association analysis, representing the magnitude of the impact on health risks per unit increase in air pollutant concentration.For PM 2.5 , the β value indicates the relative increase in health risks for each unit increase in PM 2.5 concentration.For instance, if a study finds that for every 10 μg m −3 increase in PM 2.5 concentration, the incidence of cardiovascular diseases increases by 20%, the corresponding β value would be 0.2.Thus, establishing the exposure-response relationship between air pollutants and mortality is crucial for conducting HIA.Through extensive literature review and and meta-analysis, previous studies have identified associations between PM 2.5 and premature deaths.Specifically, an annual mean increase of 1 μg m −3 in PM 2.5 concentration was found to correspond to 0.34%, 0.07%, and 0.11% in all-cause, cardiovascular, and respiratory premature deaths, respectively 20,21 .Similarly, for MDA8 O 3 , each 1 μg m −3 rise in its concentration was associated with increases of 0.10% in non-accidental mortality, 0.15% in cardiovascular mortality, and 0.20% in respiratory mortality 22 .It's important to note that the β values used in this study to assess human health risks due to PM 2.5 and O 3 are derived from the above these studies.Referring to the study from Zhao et al. 16 , PM 2.5 and MDA8 O 3 indicators were employed to estimate premature deaths across three health endpoints attributed to long-term exposure to PM 2.5 and O 3 .The calculation formulas are as follows: Here, C represents the annual average concentration of PM 2.5 and MDA8 O 3 , while C 0 denotes the safety threshold.If the concentration exceeds C 0 , it signifies potential health risks.The C 0 values for PM 2.5 and MDA8 O 3 are set at 10 μg m −3 and 26.7 ppb, respectively, based on the study by Kuerban et al. 23 .β represents the percentage increase in health effects associated with a 1 μg m −3 increase in PM 2.5 and MDA8 O 3 concentration.As previously mentioned, β values for all-cause and cardiovascular mortality attributed to PM 2.5 are 0.34% (95% CI 0.08-0.50%)and 0.07% (95% CI 0.04-0.09%),respectively 20,21 .For MDA8 O 3 , corresponding β values are 0.10% (95% CI 0.05-0.20%)and 0.15% (95% CI 0.05-0.29%),respectively 22 .The β values of respiratory mortality are 0.11% (95% CI 0.00-0.22%)for PM 2.5 and 0.20% (95% CI 0.00%, 0.43%) for MDA8 O 3 22,24 .RR represents the relative risk, while P denotes the exposed population of each city.F p denotes the mortality rate for three health endpoints.According to the study by Liao et al. 25 on municipal-level mortality rates, where detailed information regarding the F p of each city from 2006 to 2012 was provided.Considering the minimal fluctuation in F p values each year, we utilized the average F p value from their study covering the years 2006 to 2016 as the F p value for calculating the health impacts of PM 2.5 and O 3 during 2015-2019 in this study, as shown in Table 1.E represents the number of deaths related to PM 2.5 and O 3 .

Spatiotemporal distribution and monthly variation of PM 2.5 and MDA8 O 3
Figure 2 indicates the spatial pattern and average concentrations of PM 2.5 and MDA8 O 3 across various cities in the GBA over the five-year period.Overall, there was a gradual decrease in PM 2.5 concentration in each city from 2015 to 2019.Additionally, the spatial distribution of PM 2.5 remained consistent each year, exhibiting a pattern of decrease from northwest to southeast, which was consistent with previous findings by Lin et al. 26 and Miao et al. 27 utilizing satellite remote sensing technology.The highest PM 2.5 concentration was recorded in Zhaoqing (31.8-40.4μg m −3 ), followed by Foshan (29.8-39.6 μg m −3 ) and Dongguan (31.9-37.1 μg m −3 ).This phenomenon could be attributed to the fact that these cities are inland and the presence of mountains obstructs the dispersion of PM 2.5 9 .The concentrations in square brackets represent the maximum and minimum values of PM 2.5 during 2015-2019.However, coastal cities benefit from ocean breezes, which facilitate the dispersion and dilution of PM 2.5 .Furthermore, higher levels of precipitation aids in the deposition of PM 2.5 , thereby reducing its concentration in the air.Therefore, the concentration of PM 2.5 in coastal cities such as Hong Kong (18.9-27.0μg m −3 ), Macao (17.4-29.3μg m −3 ), Shenzhen (24.1-29.8μg m −3 ), and Huizhou (24.8-29.5 μg m −3 ) was relatively low.A similar phenomenon was also observed in the study by Fang et al. 18 .
MDA8 O 3 presented the opposite spatiotemporal distribution compared to PM 2.5 , with its concentration generally increasing in each city during the period between 2015 and 2019.Spatially, MDA8 O 3 concentration exhibited a decreasing pattern from east to west.Higher concentrations were observed in Dongguan (92.3-110.7 μg m −3 ), foshan (81.5-99.8μg m −3 ), and Jiangmen (73.2-104.2μg m −3 ), whereas some cities like Hong Kong (77.5-88.8μg m −3 ) and Shenzhen (80.3-93.8μg m −3 ) had lower concentrations.This disparity may be attributed to higher temperatures, stronger photochemical reactions, and larger emissions of O 3 precursors such as NO x and VOC s from ships and ports in coastal cities 10 .
To investigate the seasonal variations of PM 2.5 and O 3 , Fig. 3 illustrates their monthly average concentrations over the five-year period.While PM 2.5 exhibits minor fluctuations across different months and years, its monthly pattern generally resembles a "V" shape, with higher concentrations in winter (Dec., Jan. and Feb.) and autumn (Sep., Oct. and Nov.), and lower concentrations in summer (Jun., Jul. and Aug.) and spring (Mar., Apr. and May.).The highest concentration of PM 2.5 occurs during winter, which was attributed to increased anthropogenic emissions and unfavorable meteorological conditions 17 .Lower temperatures, reduced light intensity, shorter sunshine duration, and stable atmospheric stratification in winter facilitate the formation of a strong and persistent inversion layer.This inhibits the diffusion and dilution of PM 2.5 , leading to its continuous accumulation in the air and frequent heavy pollution events 9 .PM 2.5 levels begin to decline from January, reaching their lowest point in June, and gradually increase thereafter until December.During summer, PM 2.5 concentrations remain low due to factors such as intense solar radiation, strong atmospheric convection, and a thinner temperature inversion layer, which collectively enhance air ventilation and PM 2.5 dilution.Additionally, summer weather is typically rainy, and the wet deposition of particulate matter, along with cleaner air brought by marine monsoon, contributes to the removal of PM 2.5 11 .Studies have suggested that the concentration of O 3 in southern cities was significantly higher than that in northern cities in China 9 .In northern cities, the monthly variation of MDA8 O 3 formed an inverted V shape, with the highest concentration occurring around June 8 .Conversely, in southern cities, it exhibited a distinctive M-shaped pattern, peaking in May-June and then gradually decreasing, with a second peak in September-October 8,9 , which is consistent with the findings of this study.Regarding seasons, higher MDA8 O 3 levels were observed in autumn, followed by summer, spring, and winter.Surface O 3 is primarily produced through the photochemical reaction of precursors, a process whose rate is influenced by various meteorological conditions, including temperature, solar radiation, relative humidity, and precipitation 10 .Typically, during summer, characterized by high temperatures, ample sunshine, and dry air, the photochemical reaction of O 3 precursors intensifies, facilitating the formation of O 3 .However, our study reveals a noteworthy finding: the peak MDA8 O 3 concentration occurred in September during autumn, rather than in summer.This was attributed to the frequent precipitation in summer, which effectively inhibited the production of O 3 2 .The lowest MDA8 O 3 concentrations were observed in winter.Firstly, colder temperatures and weaker sunlight reduce the occurrence of photochemical reactions that generate O 3 .Additionally, atmospheric stability in winter hinders the mixing and dispersion of O 3 .Moreover, emissions of O 3 precursors like VOC s from plants may decrease in winter, further limiting O 3 formation.Overall, these factors contribute to lower O 3 concentrations during the winter months 10 .

Change trends of PM 2.5 and MDA8 O 3 during 2015-2019
Figure 4 illustrates the trend analysis of the two pollutants in the GBA and its corresponding cities.The annual average PM 2.5 concentrations in this area from 2015 to 2019 were 33.1 μg m −3 , 30.6 μg m −3 , 32.4 μg m −3 , 27.7 μg m −3 , and 26.1 μg m −3 , respectively, indicating an overall downward trend.Linear fitting based on the average concentration of each year over the five-year period revealed a decline rate for PM 2.5 in this region of 1.7 μg m −3 /year.Among the eleven cities analyzed, Macao (-2.8 μg m −3 /year), Foshan (-2.5 μg m −3 /year), Guangzhou (-2.1 μg m −3 /year), Jiangmen (-2.0 μg m −3 /year), and Hong Kong (-1.9 μg m −3 /year) exhibited higher   the upward trend was particularly evident in eight cities, except for Zhaoqing (+ 1.0 μg m −3 /year), Huizhou (+ 1.3 μg m −3 /year), and Dongguan (+ 1.8 μg m −3 /year).Specifically, significant increases were observed in Jiangmen (+ 6.9 μg m −3 /year), Zhongshan (+ 5.8 μg m −3 /year), Guangzhou (+ 4.5 μg m −3 /year), and Foshan (+ 4.0 μg m −3 /year).Consistent with our findings, previous studies have also indicated a shift in China's main air pollutant from PM 2.5 to O 3 since 2013 19,28 .Indeed, there exists a correlation between the overall decline in PM 2.5 and the rise in O 3 .Li et al. 19 demonstrated that a key factor contributing to the increase in summer O 3 in the North China Plain during 2013-2017 was the decrease in PM 2.5 , which enhanced surface solar radiation and  29 .Similarly, in the YRD region during the same period, Zhao et al. 17 reported a decline in PM 2.5 and an increase in MDA8 O 3 by 3.1 μg m −3 /year and 3.6 μg m −3 /year, respectively.In the BTH region, the rates of change were even more pronounced at 7.1 μg m −3 /year for PM 2.5 decrease and 5.4 μg m −3 /year for MDA8 O 3 increase.Contrastingly, in the PRD region, PM 2.5 exhibited a decreasing trend of 2.2 μg m −3 /year from 2015 to 2020, while MDA8 O 3 increased by 1.8 μg m −3 /year 30 .While the decline rate of PM 2.5 in the other 9 cities except Macao and Foshan was much lower than that observed in Beijing, YRD, and BTH regions, and the rising rate of MDA8 O 3 was comparatively lower than in the YRD and BTH regions, it is noteworthy that MDA8 O 3 levels in the GBA still reached nearly 100 μg m −3 in 2019, significantly exceeding the national average level.These findings underscore the imperative for further improvements in PM 2.5 and O 3 levels in the GBA.

Health impact assessment of PM 2.5 and O 3
Since the establishment of air quality monitoring stations in 2013, previous studies have extensively assessed the health impacts of air pollution across China [15][16][17][22][23][24] . A stud conducted by Kuerban et al. 23 found the numbers of premature deaths, cardiovascular diseases, respiratory diseases, and chronic bronchitis attributed to long-time PM 2.5 exposure in China for the year 2018 were 334,118, 70,983, 109,327, and 228,855, respectively.They decreased by 23%, 25%, 27%, and 27%, respectively, compared to 2015, reflecting China's achievements in controlling health risks from PM 2.5 in recent years.Regarding long-term exposure to O 3 in 2019, predictions indicated that health impacts estimates on all-cause mortality, respiratory mortality, and cardiovascular mortality were 181,000 (95% CI 91,500-352,000), 33,800 (95% CI 0-71,400), and 112,000 (95% CI 38,100-214,000), respectively, which increased by 53%, 55%, and 53%, respectively, compared to the year 2015 22 . Whle these studies have significantly contributed to our understanding of PM 2.5 and O 3 health risk assessment in China, it's essential to acknowledge that they uniformly applied the same mortality rate (F p ) for health endpoints across all cities in China, potentially reducing the reliability of the evaluation results.Given the differences in F p values for health endpoints across different cities, the utilization of municipal-level F p values for health endpoints in this study could yield a more accurate health risk estimate compared to previous studies.
Exposure-response coefficient (β) and safety threshold (C 0 ) are critical factors in air pollution risk assessment.In China, due to the absence of comprehensive cohort studies on long-term exposure to PM 2.5 and O 3 , there is no uniform determination of β values 20 .Consequently, different epidemiological studies have employed varying β values, leading to differing estimations of health risks [31][32][33] .For example, Feng et al. 34 and Zhang et al. 12 used different β values to estimate total mortality attributed to PM 2.5 in China for 2015, reporting 1,130,000 and 1,850,000 deaths, respectively.Additionally, Zhang et al. 24 utilized β values from Zhang et al. 21and Yin et al. 14 to calculate 205,800 (95% CI 176,200-240,000) and 121,500 (95% CI 66,200-176,221) AD caused by O 3 exposure across China in 2015, respectively.Currently, there is no theoretical explanation for C 0 .Regarding C 0 for PM 2.5 , the World Health Organization (WHO) has recommended a reference concentration of 10 μg m −314, 35 .Regarding the O 3 threshold value for short-term exposure, currently, there is no theoretical explanation.The WHO has , while a threshold of 100 μg m −3 has been deemed safe for public health by both the CAAQS Grade I and WHO 23 .In previous studies on the health risks of longterm O 3 exposure, epidemiological studies have confirmed that a threshold value of 26.7 ppb has the highest correlation with disease mortality 22 .Therefore, this study utilized it to evaluate the health risks of long-term O 3 exposure.When employing the same β and C 0 values as used in our study, Kuerban et al. 23 estimated that the total AD attributed to PM 2.5 in the 9 cities of the PRD were 20,306 and 18,877 in 2015 and 2018, respectively, which were lower than our evaluation results.However, their estimates for both CD and RD were notably higher than ours.A similar discrepancy was observed when comparing the estimation of human health risks caused by O 3 in our study with the results of Zhao et al. 16 .One potential explanation for this disparity between these studies is that our study utilized city-level F P values, whereas their studies employed the national average F P value for each city 16 .
It is imperative to acknowledge that this study entails certain uncertainties.On the one hand, the acquisition of mortality data for various cities presents challenges, leading us to rely on the average F p values reported by Liao et al. 25 for the years 2006-2012 to assess the health impacts of PM 2.5 and O 3 in GBA from 2015 to 2019.Despite the minimal annual fluctuations in F p values per city, they could still impact the estimation results of this study.On the other hand, the current distribution of air quality monitoring stations predominantly focuses on urban areas within the GBA and is limited in number.In this study, the annual average concentrations of PM 2.5 and O 3 for each city were determined by averaging the data from all monitoring stations within that city, which could also affect the accuracy of the assessment results to some extent.While spatial interpolation techniques offer insights into the spatial distribution of pollutant concentrations, their efficacy is constrained by the scarcity of monitoring stations.Additionally, the absence of crucial data such as the number of disease-related deaths across different hospitals and the spatial distribution of cases significantly impacts the estimation of health mortality.In summary, to more accurately assess the impact of atmospheric pollution on human health, it is necessary for future research to establish more air quality monitoring stations in the region.Additionally, the utilization of more precise disease data can help mitigate this uncertainty.

Conclusions
This is the first study to comprehensively assess combined pollution characterized by PM 2.5 and O 3 and its potential health impacts in the GBA.We observed a decline in PM 2.5 and a rise in MDA8 O 3 during 2015-2019, with a decline rate for PM 2.5 of 1.7 μg m −3 /year and a rise rate for MDA8 O 3 of 3.2 μg m −3 /year.The significant decrease in PM 2.5 , particularly in Macao, Foshan, Guangzhou, and Jiangmen, highlights the efforts of these cities in controlling PM 2.5 in recent years.On the other hand, Jiangmen exhibited the highest increase in MDA8 O 3 , followed by Zhongshan and Guangzhou, indicating the urgent need to implement measures to prevent O 3 pollution in these regions in the future.Compared to 2015, the estimated number of AD, CD, and RD in 2019 caused by PM 2.5 decreased by 27.6%, 28.0%, and 28.4%, respectively.In contrast, those caused by O 3 increased by 45.9%, 46.2%, and 44.2%, respectively.These findings indicate that the health benefits resulting from improvements in PM 2.5 might be offset by the health risks associated with increased O 3 levels if insufficient attention is given to O 3 control in the future.Thus, it is urgent to implement coordinated control of PM 2.5 and O 3 in the GBA.
decline rates over the five-year period.Conversely, Huizhou (-0.6 μg m −3 /year) and Dongguan (-1.0 μg m −3 /year) experienced lower declines.By 2019, although the annual average PM 2.5 concentration of all cities in the GBA fell below the level-2 Chinese Ambient Air Quality Standard (CAAQS, GB3095-2012) threshold of 35 μg m −3 , none of the cities had yet achieved the Grade I annual standards (15 μg m −3 ) specified in the CAAQS.Thus, PM 2.5 pollution remains a significant concern in this region, necessitating the implementation of more stringent air pollution control measures to enhance air quality.Contrary to PM 2.5 , MDA8 O 3 in the GBA has generally exhibited an upward trend over the past five years, with concentration of 83.8 μg m −3 in 2015, 84.6 μg m −3 in 2016, 92.4 μg m −3 in 2017, 89.4 μg m −3 in 2018, and 97.6 μg m −3 in 2019.The average rise of MDA8 O 3 over the period 2015-2019 was 3.2 μg m −3 /year.Notably,

Figure 4 .
Figure 4. Linear change trend of PM 2.5 and MDA8 O 3 in five years (The map on the right was generated by ArcGIS 10.7 https:// www.esri.com/ en-us/ arcgis/ produ cts/ arcgis-deskt op/ resou rces).

Figure 5 .
Figure 5.The estimated PM 2.5 -related health impacts in various cities during 2015-2019.

Figure 6 .
Figure 6.The estimated O 3 -related health impacts in various cities during 2015-2019.

Table 1 .
The F p value for all-cause, cardiovascular, and respiratory in each city of GBA.